“Chemobrain” or “chemofog” was originally described by the female breast cancer population, and refers to symptoms of decreased cognitive acuity described by patients. Often, these symptoms include problems with linear thought and multi-tasking. Studies have found that these symptoms can persist for years after therapy. Other studies have found that patients’ self-reported cognitive problems do not match up with how they score on formal cognitive testing. Researchers have suggested that patients may experience a “disorder of insight”, or an inability to see how well they actually do function. This study looked to evaluate perceived cognitive function with function based on formal cognitive testing in patients with colorectal and breast cancer.

428 patients were assessed in the study. Overall, 15% of patients reported major perceived cognitive impairment (12% of colorectal patients, and 33% of breast cancer patients). Over the four assessments performed for colorectal cancer patients, perceived cognitive impairment was approximately constant at baseline, 6 months, and 12 months, but appeared to decrease somewhat at 24 months. Formal testing deficit was identified in 22% of patients (22% of colorectal patients, and 14% of breast cancer patients). Interestingly, 31% of colorectal patients had deficits on formal testing at baseline. This improved to 10% at 24 months after treatment.

Perceived poor cognitive function was more closely associated with fatigue, quality of life, and depression than with deficits on formal testing. Patients who received chemotherapy perceived greater impairment, worse quality of life, and worse fatigue, but demonstrated no significant difference on formal testing from those who did not receive chemotherapy.

Correlation between perceived cognitive function and actual NP varied according to diagnosis and gender:

Among colorectal cancer patients, 71% reported normal perceived function and performed normally on formal testing. This was the case for 51% of breast cancer patients.

Among colorectal cancer patients, 7% reported impaired function, but performed normally on formal testing. This was the case for 35% of breast cancer patients.

Overall, female patients were more likely to report impairment in the setting of normal formal testing, while male patients were more likely to report normal function in the setting of deficits on formal testing.

While these results appear interesting, there are a few concerns. The formal testing used was not designed for this population and is known to be a poor test for multi-tasking”, which is a common complaint in this population. The study evaluated colorectal cancer patients over a period of time, but breast cancer patients only once. The presence of anxiety early on in the diagnosis and treatment process may have a significant affect, but was not tested.

This study demonstrates significant cognitive impairment reported by a high percentage of patients undergoing cancer treatment. The authors demonstrate that this impairment is often not detectable on classical or computer based formal testing. This finding does not decrease the importance or validity of perceived cognitive impairment, however. As the authors point out, both perceived cognitive deficit and objective deficit on formal testing are extremely important, and should be considered as separate but equally important contributions to a patient’s quality of life after cancer.